Variable orifice valve for airstream containing particulate coal

ABSTRACT

A variable orifice valve for balancing the flow of particulate coal in an airstream relative to other parallel conduits. The valve comprises a section of conduit which changes in area along its flow axis and a variable position valve element mounted within the conduit section. The valve element has a shape which proximates that of the conduit section and is movable axially to vary the annular area of the flow path around the valve element. There is no valve seat and, therefore, the valve is always open to some degree.

FIELD OF THE INVENTION

This invention relates to valves for controlling the flow of abrasivefluid mixtures such as an airstream containing particulate coal.

BACKGROUND OF THE INVENTION

A major technical problem confronted by coal-fired power-generatinginstallations such as electric utility plants is balancing the flowrates of multiple airstreams containing particulate coal. This problemarises in the design of flow paths between a coal pulverizer and acombustion chamber or “firebox” having spaced peripheral injectionpoints. The coal laden airstreams tend to follow general hydraulic flowprinciples in that they tend to choose the path of least resistance.Accordingly, parallel flow paths of different lengths with a commonentry will often exhibit substantially different flow rates resulting indifferent fuel feed rates and an asymmetrical fire ball in thecombustion chamber.

The problem is typically confronted by the use of ring-like flowrestrictors in the various parallel paths. Such restrictors are placedin the flow paths to reduce the interior diameter in the shorter,less-resistant paths. However, a restrictor size which is correct forone flow rate may not work for a different flow rate. Thus, variableorifice devices such as the gate valve described in the U.S. Pat. No.6,009,899 have been developed. Gate valves present their own problems;for one, they tend to include structures which can be extendedorthogonally across the flow path. As such, they create turbulence andeddy currents and are subject to rapid wear.

SUMMARY OF THE INVENTION

The present invention provides an improved flow rate valve forregulating and/or balancing the flow of particulate coal carried by oneor more of several parallel airstreams. As opposed to a flow restrictoror gate valve which is extended orthogonally into and/or across theairstream, the present valve is constructed by placing a wear-resistantvalve element of streamlined shape essentially centrally in a length offlow conduit having an axially varying cross section; e.g., a conicalsection. There is further provided a mechanism to move the valve elementaxially in the flow conduit between a first position where the areabetween the element and the inner wall of the conduit is a maximum and asecond position where the area is a minimum.

In one embodiment, axial movement of the valve element is effected byenergizing and de-energizing an electric motor which winds and unwinds acable extending into the interior of the flow conduit and connected tothe top of the valve element. In this embodiment the valve element ispreferably mounted on slides which are constructed of suitable materialsto withstand the abrasive action of the particulate coal/air flow. Anindicator is optionally provided to show valve element position.

In another embodiment the invention includes means for sensing aparameter such as a pressure differential between axially spaced pointsin the airstream and automatically effecting movement of the valveelement to produce a desired value of the measured parameter; e.g., apreselected pressure differential.

In both embodiments the streamlined valve element is preferably made ofan abrasion resistant material such as steel, alloys of steel, aluminumoxide, tungsten carbide, silicone carbide and the like. The preferredshape of the streamlined valve element is one having conically taperedleading and trailing surfaces of essentially mirror image shape; i.e., ashape resembling a football. The element moves axially within but doesnot touch or “seat” on the conduit inner surface or any extensionthereof.

Other applications and implementations of the present invention willbecome apparent to those skilled in the art when the followingdescription of the best mode contemplated for practicing the inventionis read in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The description herein makes reference to the accompanying drawingswherein like reference numerals refer to like parts throughout theseveral views, and wherein:

FIG. 1 is a cutaway view of a valve embodying the invention in a conduitfor particulate coal;

FIG. 2 is a side view of the valve, partly in section, in a maximum flowcondition;

FIG. 3 is a view of the valve in a minimum flow condition;

FIG. 4 is a plan view of the valve; and

FIG. 5 is a schematic diagram of an industrial application of the valve.

DESCRIPTION OF THE ILLUSTRATIVE EMBODIMENT

Referring to FIG. 1, there is shown a large metal conduit 10 for amixture of air and particulate coal, the flow direction being verticallyupward as seen in the drawing. Located in the conduit 10 and continuoustherewith is an insert 11 of varying cross-section including an annularsection 12 of maximum diameter, a tapered frusto-conical lead-in section14 and a frusto-conical exit section 16. The conduit insert 11 is joinedto the conduit 10 by welded or bolted flanged joints 18 and 20. Thevarious sections of the conduit insert are all made of a wear resistantmaterial such as high chromium steel which sections can be convenientlywelded together to form a relatively smooth seamless interior surface.The diameter of annular section 12 is substantially larger than thediameter of the conduit 10.

Opposed vertical steel ribs 22 and 24 are welded within the interior ofthe insert 11 to serve as supports and guides for a streamlined valveelement 26 having a pair of opposed slides 28 straddling the interioredges of the ribs 22 and 24 to provide guidance associated with thevertical displacement of the valve element along the axis of the insert11. The shape of the valve element 26 generally parallels the shape ofthe insert 11; i.e., the element 26 exhibits a tapered lower section 30,an annular central section 32 and a conical or tapered upper section 34which is essentially the mirror image of the lower conical section 30giving the element 26 the overall shape of a football. A tungstencarbide tip 36 is welded to the lower lead end of the element 26 forwear resistance. Mechanical stops 38 are formed on the inside loweredges of the ribs 22 and 24 to coact with the slides 28 to limit theextent of downward displacement of the element 26 relative to theconduit insert 11.

It will be seen in FIG. 1 that there is no “seat” for the valve element26. In the full open position shown in FIGS. 1 and 2, the annular areaaround the element 26 is approximately equal to the cross-sectional areaof conduit 10. In the full closed position shown in FIG. 3, the annularflow area is reduced to the extent the designer deems necessary; e.g.,20-50% or more.

Vertical movement of the valve element 26 is effected in this embodimentby means of a cable 40 which is attached to the top of the element 26 bysuitable means and which extends through the sidewall of the conduit 10to pass over a sheave 42 to the winding reel 44 of a motor drivencapstan 46 to wind up and unwind the cable 40 as desired to locate thevalve element in the proper axial position within the conduit insert 11.A bar 48 is disposed in the upper portion of the conduit to protect thecable 40 against wear. An indicator 50 is mounted to the outside of thecentral section 12 of the insert to provide visual indication of theposition of the cable 40 as a reflection of the position of the valveelement 26 along its axial travel.

As hereinafter explained with reference to FIGS. 2 through 5, the valveelement 26 can be lowered and raised to change the effective areaavailable for the airstream and particulate coal to flow through theconduit 10 thereby to balance said flow with the flow of other parallelconduits used to feed fuel to a combustion chamber in, for example, anelectrical power generating plant. Push button switches and the like canbe provided for operating the motor driven capstan 46 to achieve theappropriate valve position. In addition, valve position can beautomatically regulated in accordance with a measured parameter.

To that end, a first pressure sensor 52 is suitably mounted within theinterior of the lower portion of the conduit 10 to measure pressureP_(i). A second sensor 54 is located in the upper portion of the conduit10 to measure the outlet pressure P₀. Electrical signals representingthe two pressures are connected to respective inputs of the comparator56 in the form, for example, of a microprocessor. The comparator 56generates an electrical output which is connected to the motor drivencapstan 46 to wind up or unwind cable in a direction which tends toreduce the error signal produced by the comparator 56 to zero. In thisrespect a feedback system is provided to position the valve element 26along its path of axial travel at the optimum location to achieve thedesired pressure difference P_(i)−P₀.

The valve element is preferably made of a wear resistent material suchas steel, an alloy of steel, aluminum oxide, tungsten carbide and/orsilicone carbide. Other materials may also be used according to thedesired life of the valve element and the abrasiveness of the mixtureflowing over it. This number is compared to a reference quantityvariably inserted or programmed into device 56 and the difference usedas an “error” signal to drive device 46 in a direction which reduces the“error” signal to zero.

Referring now to FIG. 2, the valve is illustrated in the fully opened ormaximum flow position. In this condition the guides 28 are locatedwithin the maximum diameter central section 12 of the conduit insert 11;i.e., the maximum diameter of the valve element 16 is axially colocatedwith the maximum diameter of the conduit insert 11. As shown in FIG. 2this produces an annular area between the valve element 26 and theinterior surface of the conduit insert 11 which approximates thecross-sectional area of the conduit 10.

Referring to FIG. 3, the valve element 26 is shown in its lowermostposition wherein the annular section 12 of the valve element 26 iswithin the minimum diameter portion of the insert 11. The guides 28 aredisposed on the ribs 22, 24 at or near the mechanical stops 38. This isachieved by extending the cable 40 by unwinding cable from the motordriven capstan 46. The result is to minimize the annular area betweenthe belt line 32 of the valve element 26 and the interior surface of theconduit insert 11 to provide the maximum desired degree of restrictionto flow of the coal air mixture.

INDUSTRIAL APPLICABILITY

Referring now to FIG. 5, there is shown a pulverized coal fired heatingsystem comprising a conventional coal pulverizer 60 having four outputair flow conduits 62, 64, 66 and 68 connected to the four corners of atangentially fed combustion chamber or firebox 70. Because the conduits62, 64, 66 and 68 are effectively all of different lengths, variableorifice valves 72 are located in each of the conduits to preciselycontrol and regulate the flow of the coal air mixture therethrough so asto balance the flow of combustible fuel to the chamber 70. Each of thevariable orifice valves 72 corresponds in structure to the apparatusshown in FIG. 1 and includes a differential pressure measuring system 73with an output connected to an input of the microprocessor 74. Thesystem is programmed to produce essentially equal pressure differentialreadings and essentially equal flow rates in all of the conduits 62, 64,66 and 68.

While four variable orifice valves are illustrated in the four conduitsystem of FIG. 5, operable systems can be provided with fewer than fourvariable orifice valves; i.e., it may not be necessary to place avariable orifice valve in every conduit.

While the invention has been described with reference to a mechanicalcable system for varying the position of the valve element 26 within theconduit insert 11, other mechanisms including linear motors and magneticsuspension systems may be employed. Further, it is to be understood thatthe invention is not to be limited to the disclosed embodiments but, onthe contrary, is intended to cover various modifications and equivalentarrangements included within the spirit and scope of the appendedclaims, which scope is to be accorded the broadest interpretation so asto encompass all such modifications and equivalent structures as ispermitted under the law.

1. A coal fired heating system disposed between a coal pulverizer and acombustion chamber comprising: a plurality of air/coal mixture flowpaths extending essentially in parallel between an output of apulverizer and respective inputs of a combustion chamber, at least oneof said flow paths including a variable orifice valve for controllingthe flow of particulate coal and air through said path, said valvecomprising a conduit section of axially varying cross sectional area,and a streamlined valve element disposed in section and mounted foraxial displacement relative thereto between a first unseated position inwhich the area between said element and the inner wall of the varyingarea conduit is a maximum and a second unseated position where the areabetween said element in said inner wall is a minimum, said streamlinedelement presenting a minimum area lead end to said flow and across-sectional area which increases in the direction of said flow and apowered mechanism for effecting axial movement of said element betweenthe first and second positions.
 2. A coal fired heating system asdefined in claim 1 wherein at least a portion of said streamlinedelement is made of a material selected from the group comprisinghardened steel, a hardened alloy of steel, aluminum oxide, tucsoncarbide and silicon carbide.
 3. A system as defined in claim 1 furtherincluding means for sensing a flow parameter in said path andautomatically actuating said powered mechanism to cause axial movementof said element between said first and second positions in response tosaid parameter.
 4. A system as defined in claim 1 further includingmeans for sensing a pressure differential between axially spacedlocation in said at least one flow path wherein said locations are onopposite sides of said valves along said flow path, said means forsensing being adapted to produce a signal representative of saidpressure differential, said signal being connected to said mechanism foraffecting axial movement of the element.
 5. A system as defined in claim1 wherein said valve elements exhibit the conical lead surface shape, amirror image conical trailing surface shape and a centralcircumferential band of maximum diameter relative to said leading andtrailing conical shapes.